In some underground petroleum reservoirs the petroleum within the reservoir is of such heavy gravity that even at the temperature of the underground formation the petroleum is immobile and will not flow to a producing well. It has been known to inject into those formations hot liquids or steams with the objective of raising the temperature of the formation to the point where the petroleum within the formation becomes heated to the point where it is mobile enough to be able to flow into a producing well bore.
A large body of technology has developed for the generation of hot fluids or steams at the earth surface and for the transportation of those steams or fluids to the subsurface formations. Further, as the cost of energy has increased, additional attention has been paid to the efficiency of generating and transporting the hot fluids from the surface to the subsurface formation with the objective of maximizing the input of heat into the formation and minimizing the loss of heat through the conductor carrying the hot fluids from the surface to the subsurface formation.
The subsurface formations that are now becoming targets for secondary recovery or steam stimulation techniques are deeper within the earth's formations than formations that were targets years ago and the chances for loss of thermal energy has substantially increased as the well depth increases. In some of the new target formations two different subsurface formations are candidates for the treatment with hot fluids and these different formations may be separated from each other by substantial distances. Further, each formation may be subject to different injection techniques requiring sometimes different temperatures and different pressures for the injection fluids.
It is usual in the above types of injection techniques that the conducting elements that are placed within the earth formation are of a metallic structure and are placed within the formation at the ambient temperatures of the atmosphere. In the usual case wells are drilled, cased and perforated and then steam injection tubing is run into the well and packers are placed between the tubing and the casing above (and sometimes below) the perforations where the hot fluids are to be injected. After the subsurface well elements have been placed in the formation and the well is ready for steam injection, the wellhead is connected to a steam generator and the hot fluid is pumped down into the formation through the well tubing.
The present invention is directed to a downhole apparatus that is connected near the downhole end of the injection tubing to separate the hot fluids from the two concentric tubings and place the hot fluids in position for injection into the formation. The apparatus includes elements for separating the two injection zones from each other so as to permit different zones to be treated in different manners. Further, the separate tubing elements of the concentric string are independent of each other even though connected to a common element.